SENSE AREAS AND ASSOCIATION AREAS. 215 



factory tract. Within the bulb the characteristic nerve cell is 

 the so-called mitral cell. Dendrites from these cells make synapses 

 with the terminations of the olfactory nerve fibers coming from 

 the olfactory cells in the mucous membrane of the nose. These 

 synapses form conspicuous globular structures toward the periph- 

 ery of the bulb which are known as the olfactory glomeruli, a 

 name that was given to them before it was known that they are 

 composed essentially of the terminations of the dendrites of the 

 mitral cells and of the axons of the olfactory sense cells. The 

 mitral cells constitute the second neuron in the olfactory path. 

 Their axons pass posteriorly along the olfactory tracts and where 

 these tracts unite with the base of the cerebrum they terminate 

 in several nuclei composing the olfactory area. These nuclei may 

 be regarded as a primary center through which various reflex 

 effects may be obtained. The connections of these nuclei with the 

 rest of the brain are complicated and'to a large extent not clearly 

 known. But through these connections the olfactory stimuli may 

 exert a wide-spread effect upon other parts of the brain. Some of 

 the fibers from the nuclei of the olfactory area pass to the cortex 

 of the hippocampal lobe and especially to the gyrus at the tip 

 known as the uncinate gyrus. This gyrus and the contiguous 

 areas constitute, therefore, the cortical termination of the olfac- 

 tory path; the so-called cortical center for smell. In the lower 

 vertebrates, fishes and amphibia, the larger part of the forebrain 

 is connected with the olfactory paths, and we must assume that 

 originally this sense played a dominant part in controlling the 

 relations of the animal to its environment. In man and the higher 

 mammals the olfactory portions of the cerebrum, which are some- 

 times grouped together under the name Rhinencephalon, are 

 relatively much less important, but they still constitute a large 

 area embracing such structures as the hippocampal convolution, 

 gyrus dentatus, the fimbria, the fornix and septum, the mam- 

 millary and habenular bodies, the anterior commissure, etc. 



The Cortical Center for Smell.— So far as the histological 

 evidence goes, it tends to show that the chief cortical termination 

 of the olfactory paths is found in the hippocampal convolution, 

 especially its distal portion, the uncus. The experimental evi- 

 dence from the side of physiology points in the same direction. 

 Ferrier states that electrical stimulation in this region is followed 

 by a torsion of the lips and nostrils of the same side, muscular 

 movements that accompany usually strong olfactory sensations. 

 On the other hand, ablations of these regions are followed by de- 

 fects in the sense of smell. The experimental evidence is not very 

 satisfactory, owing to the technical difficulties in operating upon 

 these portions of the brain without at the same time involving 

 neighboring regions. There is some clinical evidence also that 



